1. Field of the Invention
The present invention generally relates to laser marking of objects and, more particularly, to a rapid marking of the objects and to a rapid changeover between marks of successive objects.
2. Description of the Related Art
Lasers have been used to mark a great variety of objects and materials, for example, diamonds and other hard materials, as described, for example, in U.S. Pat. No. 4,392,476 and U.S. Pat. No. 4,467,172 where relative movement between a laser beam and a diamond surface is performed, and in U.S. Pat. No. 5,149,938, U.S. Pat. No. 5,410,125 and U.S. Pat. No. 5,573,684 where a mask, which is preformed with a cutout that defines a marking, is positioned between a laser and an object to be marked. Lasers have also been used to mark electrical wires, medical parts, consumer products, automotive parts, and, generally speaking, anything requiring to be identified and tracked.
The relative movement between the laser beam and the object is typically performed under computer control and takes a finite, but non-negligible, time to complete. Many objects are marked when mounted in succession on a moving conveyor belt. The conveyor belt cannot be stopped or paused to permit marking to occur. Even if an object is not on a moving conveyor belt, but is held stationary in a fixture, there are times when the amount of information to be marked takes a considerable time to perform, for example, when marking a two-dimensional bar code symbol such as Data Matrix(trademark), or a bit-mapped image or logo.
In the case where a mask is used with a preformed cutout, one mask can only produce a single marking. All objects are therefore marked with the same marking. To change the marking, one must physically substitute another mask with a different preformed cutout. This is not a practical solution where a multitude of objects is to be differently marked, for example, by incremental numerical markings, since it would require the manufacture and substitution of a corresponding multitude of masks, all involving a considerable time to perform.
Accordingly, it is a general object of this invention to rapidly mark an object.
More particularly, it is an object of the present invention to rapidly change markings on successive objects to be marked.
Still another object of the present invention is to mark objects in a time-efficient manner.
It is yet another object of the present invention to mark objects with a great amount of information without incurring long marking times.
In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention resides in an arrangement for, and a method of, marking an object. The object can be virtually anything requiring to be identified. The invention comprises a source, such as a laser, for emitting a laser beam having a cross section along a path toward the object at a power level sufficient to mark the object, an optical modifier in the path for optically modifying the cross section of the beam incident on the modifier, including a plurality of optical modifying elements each having an optical property and being switchable between optical states to vary the optical property, and a controller for switching at least one of the elements to at least one of the states to change the cross section of the beam leaving the modifier.
In one preferred embodiment, the modifier is a liquid crystal device, and each of the elements is a liquid crystal cell containing a liquid switchable upon application of an electrical, or magnetic, or electromagnetic, external field between a light-transmissive state in which the beam passes through a respective element, and an opaque state in which the beam is prevented from passing through, or is blocked by, the respective element. The controller selects the state of each of the cells. The desired marking is formed by switching selected ones of the cells to the light-transmissive state so that the light beam passes through the light-transmissive cells, and is blocked by the opaque cells. The light-transmissive cells define the shape of the marking.
In another preferred embodiment, the modifier is a microelectromechanical system (MEMS), and each of the elements is a reflector or a micromirror tiltable upon application of an electrical, or magnetic, or electromagnetic, external field between a first state in which the beam impinging on a respective reflector is directed along the path, and a second state in which the impinging beam is directed away from the path. The desired marking is formed by switching selected ones of the reflectors to the first state so that these selected reflectors define the shape of the marking.
Once the selected elements have been switched to the light-transmissive or the first states, a single output pulse of the laser is sufficient to mark the object. This pulse lasts on the order of femtoseconds to several seconds as opposed to the prior art techniques of conducting relative movement between a laser beam and an object which can take minutes, in some cases, or of replacing masks which can likewise take many minutes to perform. The switching of the selected elements also is conducted in fractions of a second, or in seconds.